Integrating zinc oxide nanoparticles with growth regulators for improved micropropagation efficiency, microstructural adaptations, and root cork cell differentiation in Coleus forskohlii (Willd.) Briq.
摘要
This study aimed to investigate the impact of exogenous Zinc oxide nanoparticles (ZnO NPs) and phytohormonal combinations on in vitro propagation and morpho-structural developmental responses of Coleus forskohlii. The study also aimed to incorporate the residual morpho-anatomical effects of ZnO NPs observed during ex vitro rooting and acclimatization and to provide a robust platform for mass propagation of this medicinal plant. Nodal shoot segment explants (n = 24 explants per treatment × 3) were cultured on the Murashige and Skoog (MS) medium containing 6-benzylaminopurine (BAP), or N6-furfuryladenine (Kinetin/Kn). The highest shoot induction (98.6%) was achieved on MS medium supplemented with 0.4 mg L−1 BAP (6.0 ± 0.58 shoots with 3.7 ± 0.15 cm average length). High frequency shoot proliferation (17.0 ± 0.58 shoots with 5.0 ± 0.12 cm length) was observed on MS medium supplemented with 0.3 mg L−1 BAP and 0.15 mg L−1 α-naphthaleneacetic acid (NAA). The addition of 20.0 mg L−1 ZnO NPs, along with optimal growth regulators (PGRs), increased the rate of proliferation (23.0 ± 1.16 shoots with a length of 6.4 ± 0.23 cm), leaf area (2.2 × 1.5 cm), and stem width (3.0 mm), resulting in the improved qualitative morphology and quantitative features of shootlets. The combined effects of growth regulators and ZnO NPs on the measured traits were highly significant (p ≤ 0.05) at the proliferation stage, which were further supported by the improved microstructural parameters (mechanical, photosynthetic, and vascular tissues) of leaves, stems, and roots as compared to the control. Ex vitro rooting of shoots was achieved with 100.0 mg L−1 indole-3-butyric acid (IBA) and being treated for 5 min. The rooted plantlets were then transferred to a greenhouse for further hardening and acclimatization. The root anatomy of acclimatized plantlets that were derived from ZnO NP treatments exhibited enhanced anatomical development, including the differentiation of phellem (cork) cells (site of forskolin biosynthesis), resulting in a high survival rate of 97.2%. This streamlined protocol provided a robust platform for the rapid production of C. forskohlii, facilitating both ex situ conservation and commercial exploitation for its bioactive constituents.